This invention relates to a cellulosic filler and a thermoplastic resin composition containing the same. More particularly it relates to a cellulosic filler heat-treated with glyoxal and a thermoplastic resin composition containing the same.
Heretofore, a number of attempts to blend cellulosic fillers with thermoplastic resins have been made in order to improve the stiffness, resistance to molding shrinkage, resistance to thermal deformation, coating properties, etc. of the thermoplastic resins.
Cellulosic fillers, however, usually contain moisture around 10% by weight and even when dried by a hot air-circulating dryer at 110.degree. C. for 2.about.3 hours, the fillers still contain 4.about.7% by weight of moisture; thus when such cellulosic fillers are blended with thermoplastic resins and the resulting blend is molded, the moisture contained therein is rapidlyliberated at molding temperatures of 160.degree. C. or higher to generate steam, resulting in cavities or blisters in the molded product. Occurrence of such cavities deteriorates the physical properties of the molded product such a mechanical strength, stiffness, resistance to thermal deformation, etc., while occurrence of blisters becomes a cause of deforming its apparent shape; thus thermoplastic resins having cellulosic fillers blended therein have not yet been sufficiently practically used.
Further, since moisture-containing cellulosic fillers are tough, they are disintegrated with difficultly in processing steps such as in an extrusion molding step; hence a problem occurs whereby it is necessary to use particles which are finely disintegrated to a particle size of 60 to 120 mesh in advance and thus such a disintegration step is required.
The present inventors have made extensive research in order to solve the above problem directed to thermoplastic resins having cellulosic fillers blended therein, and as a result, have found that the above problem can be solved by using cellulosic fillers heat-treated with glyoxal.